The invention relates to a carrying arm arrangement for moving and positioning at least one magnetic head over a surface of a rotatable magnetic disc of a magnetic-disc storage apparatus for the storage and reproduction of data in digital form, and more particularly to such an arrangement including a carrying arm and a plurality of magnetic heads each connected to the arm.
Magnetic disc storage equipment comprising one or a plurality of rigid magnetic discs each serving for the storage and reproduction of data in digital form on at least one side and generally on both sides is employed on a large scale as peripheral equipment for data processing apparatus such as computers.
The magnetic discs rotate with a high speed, for example 3600 revolutions per minute. The magnetic heads, which are secured to ends of the carrying arm arrangements, are moved over the surfaces of the magnetic discs to locations which are preselected by the data processing apparatus in order to store data in a specific track on the magnetic disc or in order to reproduce data from said track. The carrying arm arrangements comprise carrying arms which are either linearly movable in a radial direction or pivotable about a pivotal axis parallel to the axis of rotation of the magnetic discs. The magnetic heads should be moved as fast as possible over the magnetic discs in order to minimize the time required for locating the correct track and storing or reproducing the data. The magnetic discs are manufactured with an extremely high degree of flatness. The magnetic heads float on a very thin film of air very close to the surface of the magnetic discs.
In many cases, each magnetic head is secured to a resilient magnetic head carrier in order to obtain the mobility which permits the magnetic head to float on the air film and in order to provide a resilient load which exerts an accurately defined pressure on said head. In order to minimize the external dimensions of magnetic disc storage equipment, the various manufacturers attempt to arrange the magnetic discs as close as possible to each other. The carrying arm arrangements, especially when they are interposed between two magnetic discs, should, therefore, be as flat as possible and move as close as possible to the magnetic disc surface. It is obvious that the carrying arm should never touch the magnetic disc surface because this would render the magnetic disc unserviceable.
Carrying arm arrangements for magnetic disc storage equipment should, therefore, be manufactured with the necessary precision.
A swing arm arrangement of the type mentioned in the opening paragraph is known from U.S. Pat. No. 4,150,407. The known swing arm arrangement comprises one or more aluminum swing arms in the form of bifurcated levers which are pivotable about a pivotal axis disposed between two ends. Arranged near the one end of each swing arm is a magnetic head unit comprising the magnetic head and a resilient magnetic head carrier. The carrier is rigidly connected to the carrying arm. On the other end of the swing arm, a control coil is arranged. Said coil belongs to electromagnetically and electrically controllable actuating means by means of which it is possible to impart a pivotal movement about the pivotal axis of the swing arm to said arm, so as to enable the magnetic head to be moved over the magnetic disc in a substantially radial direction.
In a version of the known arrangement comprising a plurality of swing arms, said arms are arranged above and spaced from one another and they are combined to form an assembly of swing arms which are pivotable about the pivotal axis. Each swing arm carries a separate flat control coil, so that these coils are also combined to form an assembly of control coils which are spaced from each other. The assembly of swing arms is journalled on a frame by means of a bearing arrangement which comprises two ball bearings and a bearing pin on which the inner races of the ball bearings are fixed by suitable means so as to be axially spaced from each other. The outer races of the ball bearings are fitted in a bearing housing which is screwed to the deck of the magnetic disc storage apparatus; a compression spring between the outer races eliminating the axial bearing play. The control coils move in a permanent magnetic stator.
Said stator comprises a stator frame and a plurality of flat, axially magnetized permanent stator magnets which are connected to the stator frame and between which air gaps are formed for each flat control coil, so that each control coil is movable in an axial permanent magnetic field within an air gap formed between permanent stator magnets. On each side of the stator, iron stator end plates are arranged which extend over the interposed control coils and stator magnets and on which the outermost stator magnets are mounted, so that the axial permanent magnetic stator fields are closed via the iron stator end plates. Each control coil comprises turns of an electrically conductive material wound onto a plastics coil former which forms one structural unit with the control coil by means of a synthetic resin. The control coils are connected to the swing arms by clamping and glueing on the ends of the swing arms which are remote from the magnetic heads.
A swing arm arrangement of the type mentioned in the opening paragraph is also known from U.S. Pat. No. 4,196,456. This known swing arm arrangement bears great resemblance to the previously mentioned known swing arm arrangement except that the control coils are not arranged directly on the swing arms but are stacked on a bearing bush as separate units. The bearing pin is fixed.